Known is a technique for compressing (encoding) text data using a dictionary. For example, a word matching with a dictionary included in a computer that performs compression processing is replaced with a previously associated code in the dictionary. Conventional technologies are described in Japanese Laid-open Patent Publication No. 5-181641 and Japanese Laid-open Patent Publication No. 2000-201080, for example.
The number of words held in a dictionary included in a computer that performs compression processing is limited, so that a word not registered in the dictionary may appear in text data as a compression target. The number of held words may be different depending on a scale of the computer. For example, a dictionary having a small amount of data is used in a terminal device such as a cellular telephone and a smartphone to suppress a storage capacity to be used. On the other hand, a large-scale dictionary holding various pieces of information is used in a server computer such as a cloud system to perform data mining, for example. In this way, the number of words held in the dictionary may be different between the terminal device and the cloud system.
Expansion processing for compressed data on which compression processing is performed is not necessarily performed by the same computer as the computer that has performed the compression processing. Thus, the dictionary used for compression processing is limited to a dictionary that can be utilized in any computer that can perform expansion processing. For example, when compressing data to be also expandable by the terminal device, the cloud system compresses the data using a dictionary that can be utilized in the terminal device even when a large-scale dictionary can be utilized. Due to this, the compressed data can be expanded by the terminal device. However, such compressed data is not effectively utilized in other computers including the large-scale dictionary.